Quiet-time low-energy ion fluxes in the 23rd and 24th solar cycles at 1 AU

Abstract: The relative abundances of 3He, 4He, C, O and Fe ions in the energy range 0.04 to 1 MeV/nucleon and the energy spectra of 3He and Fe are investigated during quiet-time periods in the 23rd and 24th solar cycles using ACE/ULEIS data. Quiet-time fluxes of suprathermal ions with low first ionization potential (FIP) ≤ 10 eV were found to exhibit higher variability than those with high FIP (above 10 eV). The quiet periods selected were divided into three groups according to the value Fe/O in the energy range of ~40-320 keV/nucleon. In the 23rd SC except for the minimum the Fe/O ratio was within the interval of values comparable with those of impulsive SEP events or was near the mean abundance in solar corona. During solar minimum Fe/O was close to the solar wind values. Ions of these 3 groups originate from different seed particle populations: ions of the upper solar corona, those accelerated in impulsive micro SEP events, ions of quiet corona and solar wind ions, respectively. Noticeable differences in the energy spectra and energy dependences of relative abundances of suprathermal ion fluxes were found between SC 23, the 2008-09 minimum and the first 4 years of SC 24